Icosahedral Carborane Superacids and their Conjugate Bases Comprising H, F, Cl, and CN Substituents: A Theoretical Investigation of Monomeric and Dimeric Cages

Abstract

Theoretical investigation of the H(CHB11X11) (X=H, F, Cl, CN), H(CHB11XnY11‐n) (X,Y=F, Cl; n=1,5), and dimeric (H(CHB11X11))2 (X=F, Cl) carborane superacids performed at the B3LYP/6‐311++G(d,p) theory level revealed the similarity of their equilibrium structures and the possibility of nearly barrierless hydrogen atom migration among the substituents attached to one side of the icosahedral CB11 cage. The vertical electron detachment energies predicted at the OVGF/6‐311++G(3df,2pd) theory level for the conjugate bases (CHB11X11)− were found to span the 5.82–9.00 ev range. The acid strengths (manifested by the Gibbs free deprotonation energies spanning the 213–266 kcal/mol range) predicted for the icosahedral H(CHB11X11) carborane systems confirm their superacidic properties which might be increased even further by the attachment of the second carborane H(CHB11X11) unit that leads to a dimeric structure mimicking a part of an experimentally observed H‐bridged polymeric chain. The Gibbs free deprotonation energy of the dimeric (H(CHB11Cl11))2 acid was predicted to be smaller by 17 kcal/mol than that of the corresponding monomeric H(CHB11Cl11) acid.

Electron Propagator Theory of Vertical Electron Detachment Energies of Anions: Benchmarks and Applications to Nucleotides

“…The importance of electron correlation in determining reliable electron detachment energies of superhalide anions was emphasized at an early stage . Metal (M with m valence electrons) halide (X) anions with the general formula M i X mi +1 – that exhibit delocalization of Dyson orbitals over many halogen centers have been especially frequent objects of study. − Extensions to alternative electronegative ligands have been shown to be feasible. − Even organic ligands such as carboxylates and amino acids or fluoroborate tripods were discovered to be suitable for constructing superhalogens. − Connections between the search for more powerful superhalogens with record-setting electron detachment energies and the optimization of superacids with superlative Brønsted acidity have been identified after analysis of electron propagator calculations on icosahedral carboranes. , OF 3 – turns out to be a superhalogen, as do large H n F n +1 – clusters with extraordinarily large electron detachment energies, alkali-metal complexes with borane, HF–MF n – clusters, boron–nitrogen fluoride oligomers, NaCl clusters, noble-gas fluorides, BO 2 – , and (by a narrow margin) BS 2 – . Direct calculation of improvements to canonical Hartree–Fock energies has proven to be a crucial advantage in superhalide clusters where the qualifying electron detachment energy does not correspond to the highest occupied molecular orbital. − For example, in clusters with CN ligands, the order of σ and π orbitals may be reversed by electron correlation.…”

Caralumane Superacids of Lewis and Brønsted Character

“…Recently, the Reed group reported results concerning protonation of highly inert species, such as carbon dioxide, using carborane superacids . Many other groups have also contributed to the field by investigating various carborane acids and their conjugate bases. − In addition, the Skurski group has recently shown the large mobility of the acidic proton in certain carborane acids and a significant increase of their acid strength upon dimerization …”

“…40−46 In addition, the Skurski group has recently shown the large mobility of the acidic proton in certain carborane acids and a significant increase of their acid strength upon dimerization. 47 1.3. Lewis and Brønsted Superacids Treated Here.…”

Predicting novel strong acids of plumbylene at theoretical levels

“…[ 19 ] Various Lewis‐Brønsted superacids have been reported at theoretical levels. [ 20–27 ] Strength of Lewis‐Brønsted superacids containing In, Sn, and Sb has been investigated, which employs the B3LYP, QCISD, and OVGF methods. [ 28 ] A new series of superacids was achieved by protonation of B n H 3 n +1 − superhalogen anions, using an MP2/6‐311++G(d,p) basis set.…”